1. Field of the Invention
The invention relates to a driven axle assembly which comprises
a centre housing, PA1 suspension elements connecting the centre housing to the vehicle, PA1 a main drive arranged in the centre housing, PA1 side drives arranged on outer ends of the centre housing, and PA1 wheel hub units connected to the side drives, respectively, wherein a portal distance is provided between a longitudinal axis of a differential gear unit arranged in the centre housing and a longitudinal axis of the wheel heads. PA1 a centre housing, PA1 suspension elements connecting the centre housing to the vehicle, PA1 a main drive being arranged in the centre housing and including a PA1 differential gear unit, PA1 side drives arranged on outer ends of the centre housing, and PA1 wheel hub units connected to the side drives, respectively,
2. Description of the Related Art
Axle assemblies with this so called portal arrangement are more widely used nowadays to enhance public transport, to speed up the passenger traffic, to make the entry and exit easier in the case of motor busses. The outstanding advantage of the portal arrangement is in that the floor height of the vehicle can be as low as 320 to 350 mm measured from the ground level so there is only one step needed to step up from the pavement level. However, there are certain difficulties with driven rear axles of the vehicles since not only the required drives must find space, but sufficient stability and rigidness must be provided and the connections to the vehicle frame must be stable enough as well.
In case of known axle assemblies (as it is described inter alia in GE patent specification No. 340 27 806), the main drive is put aside as far as possible from the longitudinal axis of the vehicle. Onto the differential being a part of main drive, a pair of bevel and disk gears is attached, wherefrom the revolution is led to the side drives. Thus, increase of the torque and reduction of numbers of the rotation are carried out in two steps. The portal distance can be measured between the longitudinal axis of the differential arranged in the centre housing and the longitudinal axis of the outlet axle shafts, i.e. that of the hub units: this is the measure with which the floor level of the vehicle can be made lower in comparison to that of the vehicle with a conventional axle assembly.
In the prior art proposals, the support and suspension elements are not parts of the axle assembly. In the conventional arrangements, for example, on each side, 2.times.3 pieces that is altogether 12 pieces, of massive connecting eyes are provided on housings of the side drives, and the choice, outline and attachment of these support and suspension elements are left over to the producer of the motor busses. The bus producers form these suspension elements as welded constructions made of more than one piece, these pieces are then fixed to each other as well as to the housings of the side drives and the frame of the vehicle by threaded connections. Onto this support system of beams screwed to each other, the air springs and the shock absorbers of the vehicle are attached, too.
In practice, it proves to be unfavourable per se that the support and suspension elements are constructed from more than one piece. At each and every threaded connection, the strength of the bearing construction is drastically reduced, and at the same time, the screwed connection is a stress collecting area. In known solutions, for example, four separate elements are screwed onto the axle assembly. It has been proven, as well, that even the most special threaded connections get inevitably loose from time to time, which is outmostly inconvenient in terms of safety of the conventional axle assemblies. At the screwed connections, the closed beams change to be an open one, and this further reduces the strength and stability of conventional suspension elements.
It cannot be disregarded that, as a result of what has been said above, the known support and suspension elements must be over-dimensioned and sufficient stability must be provided at the screwed connections as well. This makes the assembly not only a more complicated one but the self weight of the axle assembly will be increased, too.
In the bus construction industry, the tendency can be observed most recently, that the bus producers are not willing to manufacture the support and suspension elements by themselves and it is inconvenient to procure them from outside suppliers. Thus, the still unsolved need is more and more urgent that the producer of axle assemblies should provide their products as a complete construction having all fasteners, and suspension elements mounted on them ready for installation.